Regulation of Rho/ROCK signaling in airway smooth muscle by membrane potential and [Ca ]i

Liu, Caiqiong, Jianmin Zuo, Evi Pertens, Peter B. Helli, and Luke J. Janssen. Regulation of Rho/ROCK signaling in airway smooth muscle by membrane potential and [Ca ]i. Am J Physiol Lung Cell Mol Physiol 289: L574–L582, 2005. First published June 3, 2005; doi:10.1152/ajplung.00134.2005.—Recently, we have shown that Rho and Rho-activated kinase (ROCK) may become activated by high-millimolar KCl, which had previously been widely assumed to act solely through opening of voltage-dependent Ca channels. In this study, we explored in more detail the relationship between membrane depolarization, Ca currents, and activation of Rho/ ROCK in bovine tracheal smooth muscle. Ca currents began to activate at membrane voltages more positive than 40 mV and were maximally activated above 0 mV; at the same time, these underwent timeand voltage-dependent inactivation. Depolarizing intact tissues by KCl challenge evoked contractions that were blocked equally, and in a nonadditive fashion, by nifedipine or by the ROCK inhibitor Y-27632. Other agents that elevate intracellular calcium concentration ([Ca ]i) by pathways independent of G protein-coupled receptors, namely the SERCA-pump inhibitor cyclopiazonic acid and the Ca ionophore A-23187, evoked contractions that were also largely reduced by Y-27632. KCl directly increased Rho and ROCK activities in a concentration-dependent fashion that paralleled closely the effect of KCl on tone and [Ca ]i, as well as the voltage-dependent Ca currents that were measured over the voltage ranges that are evoked by 0–120 mM KCl. Through the use of various pharmacological inhibitors, we ruled out roles for Ca /calmodulin-dependent CaM kinase II, protein kinase C, and protein kinase A in mediating the KCl-stimulated changes in tone and Rho/ROCK activities. In conclusion, Rho is activated by elevation of [Ca ]i (although the signal transduction pathway underlying this Ca dependence is still unclear) and possibly also by membrane depolarization per se.